Single-cylinder and double-cylinder circular knitting machines for hosiery or the like are known.
Single-cylinder circular knitting machines comprise substantially a needle cylinder which has a vertical axis and on the lateral surface of which there are a plurality of axial slots, each of which accommodates a needle which can be actuated with an alternating motion along the corresponding axial slot in order to form knitting. The needle is provided generally with a heel which protrudes radially from the corresponding axial slot of the needle cylinder, and the needle is actuated by providing a plurality of needle actuation cams which are arranged around the needle cylinder and define, as a whole, paths which are shaped with rising portions, parking or horizontal portions, and descending portions, which can be followed by the heel of the needles when the needle cylinder is actuated with a rotary motion about its own axis with respect to the needle actuation cams.
Double-cylinder circular knitting machines for hosiery generally comprise a lower needle cylinder which has a vertical axis and an upper needle cylinder which is arranged above and coaxially with respect to the lower needle cylinder, such cylinders being actuatable rigidly with each other with a rotary motion about the common axis.
A plurality of axial slots are formed on the lateral surface of the lower needle cylinder and on the lateral surface of the upper needle cylinder. The axial slots of the upper needle cylinder are aligned with the axial slots of the lower needle cylinder. A slider is accommodated in each of the axial slots of the lower needle cylinder and in each of the axial slots of the upper needle cylinder. Between the two needle cylinders, i.e., in the knitting region, in each of the axial slots there is a needle which is provided with two tips or heads, respectively an upper head and a lower head; depending on whether one wishes to provide plain stitches or purl stitches, such needle is moved into the lower needle cylinder so that its knits with its upper tip or into the upper needle cylinder so that its knits with its lower tip.
Since the needle does not have a heel, it is actuated by means of the slider arranged in the lower needle cylinder or by means of the slider arranged in the upper needle cylinder, depending on whether it has to form plain or purl stitches.
The sliders currently used in double-cylinder circular knitting machines for hosiery are constituted generally by an elongated laminar body, which has a first longitudinal side designed to rest on the bottom of the axial slot formed on the lateral surface of the lower needle cylinder or on the lateral surface of the upper needle cylinder.
Such sliders are further provided with two heels, which are mutually spaced along the longitudinal extension of the slider and protrude transversely from a second longitudinal side of the slider which lies opposite the first longitudinal side.
These heels are used to produce the movement of the slider along the corresponding axial slot of the lower or upper needle cylinder so as to cause the actuation of the needle associated with said slider in the various types of knitting of the machine or to transfer the needle from one needle cylinder to the other.
The slider is further provided, on its first longitudinal side, i.e., on its side directed towards the bottom of the axial slot within which it is accommodated, with a hook-shaped tab, which engages the lower head of the needle or the upper head depending on whether the slider is in the lower needle cylinder or in the upper needle cylinder.
Around the lateral surface of the lower needle cylinder and around the lateral surface of the upper needle cylinder there are a plurality of slider actuation cams, which define a series of paths with which the heels of the sliders engage when the needle cylinders are actuated with a rotary motion about their axis with respect to said cams. The paths defined by the cams are shaped so as to cause the movement of the sliders along the axial slots of the needle cylinders in which they are accommodated and consequently cause the actuation of the needles that are associated therewith.
In order to vary the actuation of each needle and therefore vary the type of knitting that the needle produces, it is necessary to actuate the transfer of its heel or of the heel of the slider that actuates it from one path to another path of the corresponding actuation cams, and this is achieved generally by providing, inside each axial slot, below the needle in single-cylinder circular machines or below the slider in the lower needle cylinder in double-cylinder circular machines, a sub-needle or selector, which is also provided with one or more heels which can protrude radially from the lateral surface of the needle cylinder in order to engage selector actuation cams which are also arranged around the lateral surface of the needle cylinder in single-cylinder circular machines or of the lower needle cylinder in double-cylinder circular machines.
The selectors can generally oscillate on the radial plane of the needle cylinder on which they lie in order to pass from an active position, in which they protrude from the corresponding axial slot of the needle cylinder or of the lower needle cylinder with at least one of their heels so as to engage the selector actuation cams, to an inactive position, in which they are embedded with their heel or heels within the corresponding axial slot so as not to engage the selector actuation cams, or vice versa.
The selector actuation cams have rising portions and descending portions so as to cause, as a consequence of the rotation of the needle cylinder about its own axis with respect to the selector actuation cams, when a heel of a selector engages them, the rising movement of the needle or of the slider that lies above in order to produce its direct actuation or the transfer of its heel from one path to another among the paths defined by the needle actuation cams or by the slider actuation cams or to allow the descending movement of the needle or of the slider which is usually caused by the needle actuation cams or by the slider actuation cams.
The passage of the selectors from the active position to the inactive position is actuated by means of selection devices which laterally face the needle cylinder of the machine and which, by means of the selectors, are capable of varying the actuation of the needles and therefore of varying the knitting that can be produced.
In currently commercially available circular machines, the intervention of the selectors, by means of the selection devices and the selector actuation cams, in order to cause a variation of the path followed by the heels of the needles or of the sliders, can occur only in certain conditions of mutual arrangement of the selector and the needle or the slider that is in the same axial slot, and this imposes severe constraints and limitations in the design of the set of actuation cams of the needles or sliders and selectors.
In currently commercially available circular machines, in order to overcome these limitations and increase the operating possibilities of the machines, very often, between the needle actuation cams and between the slider actuation cams there are also additional cams which can move on command, with respect to the fixed element that supports them, known as cam box, along a radial direction with respect to the needle cylinder, so as to pass from an active position, in which they are close to the needle cylinder in order to be engaged by the heels of the needles or of the sliders, to an inactive position, in which they are spaced from the needle cylinder so as to not interfere with the heels of the needles or of the sliders and vice versa.
The presence of these movable cams and of the corresponding actuators, which is necessary in order to produce the various kinds of knitting, has the problem of increasing considerably the complexity of the structure of the entire machine.
Moreover, the presence of these movable cams forces the provision, on board the machine, of an appropriately provided actuation program, which intervenes if an accidental stop of the machine occurs due to a lack of electric power supply and restores the correct position of the movable cams before knitting resumes, since if the machine were to restart without first restoring the correct position of the movable cams the heels of the needles or of the sliders might break.
In practice, the presence of these movable cams makes it necessary to provide the machine with electronic programs which store the position of the movable cams when the electric power supply is interrupted, and this constitutes a further complication in the manufacture of the machine.